Thermoplastic polyurethane resins (TPU) are generally produced by reacting a polyol, a diisocyanate and a glycol chain extender. The properties of these resins depend to a large extent on the relative amounts of the reactants. These resins have been blended with other thermoplastic resins to produce compositions having a variety of properties making them suitable for a host of applications. Although non-polar polyethylene, or polypropylene, and polar TPU have been viewed as incompatible one with the other, such blends are desirable and some, containing small amounts of the olefins have been reported.
For instance, U.S. Pat. No. 3,929,928 indicates that mill blending of a thermoplastic polyurethane with polyethylene results in severe plate-out due to incompatibility of the two polymers. Researchers have reported in Organic Coatings Plastics Chemistry, Vol. 40, page 664 (1979) that it was impossible to prepare with a roll mill useful test specimens at any polyurethane/polyethylene blend ratios. Similarly, Walker's Handbook of Thermoplastic Elastomers, Section 5.4.17, reports that low density polyolefin modifications of polyurethane polymers must be maintained below 3 percent to avoid adverse effects due to incompatibility of the two polymers. Although U.S. Pat. No. 3,272,890 purports useful blends of polyolefin and soft polyurethane polymers, such blends are polyolefin based, containing less than 25 percent by weight polyurethane polymer where polyurethane polymer contents above 25 percent are incompatible and cannot be molded into useful plastic containers. Crystalline high density polyethylene or polypropylene polymeric blends are even more difficult to prepare due to incompatibility of the crystalline polyolefins with polyurethanes. Useful blends of thermoplastic polyurethane elastomers containing less than 15 percent by weight neutralized ethylene/carboxylic acid copolymers are disclosed in U.S. Pat. No. 4,238,574 to provide elastomeric blends useful in blow-molding operations.
U.S. Pat. No. 4,975,207 disclosed a blend of TPU and a carbonyl-modified polyolefin. U.S. Pat. No. 5,623,019 disclosed a compatibilized composition containing TPU and polyolefin. A particularly structured copolymer which contains blocks of monoalkylene arene and conjugated diene is said to compatibilize the components.
U.S. Pat. No. 4,990,557 disclosed the preparation of mechanically stabilized compatible blends of TPU and an at least mostly crystalline polyolefin by a high shear mixing of a melt of these polymers.